A CMOS image sensor does not follow a typical semiconductor manufacturing process. A hydrogen anneal (sinter) process, for improving a low illumination characteristic, is not performed after forming a passivation oxide layer, but is performed after forming a passivation nitride layer. This causes various problems, which involve a nitride layer susceptible to inter-layer stress in the areas near the edges of a wafer.
Problems of related technologies will be described with reference to FIGS. 1A to 1I. FIG. 1A is a sectional view showing a process in which a passivation oxide layer 120 and a passivation nitride layer 130 are deposited after forming a pad 110. Unlike the main central region of the wafer, the areas near the edges of the wafer have irregular residual layers 100 formed through several photo processes due to a wafer edge treatment in a photo process. The edge area has an inferior adhesive binding due to these irregular residual layers 110. In this state, the hydrogen anneal process, which is a heat treatment process requiring a proper ratio of oxygen gas to nitrogen gas, is performed on the CMOS image sensor. During the heat treatment process, the inter-layer stress of the nitride layer 130 at the edge of the wafer is increased. Fluorine ions included in a fluorinated silicate glass of the residual layer 100 are lifted up. The nitride layer 130 at the edge of the wafer is peeled in the shape of a circle, which is called a wafer edge peeling. In addition, during the heat treatment process, particles peeled from the wafer edge area may move to a pixel region in the wafer.
FIG. 1B shows the wafer edge peeling 140 created after the hydrogen anneal process and particles transferred to the pixel region in the main area of the wafer. Since the transferred particle is circular in shape, the particle is called a circle defect 145.
Referring to FIG. 1C, to remove the circle defect 145, a scrubbing process is performed. A pad area 110 is exposed through a photolithography process. Subsequent cleaning and pad treatment processes include a pad ashing step, a solvent cleaning step, and a final curing step. Although the scrubbing and cleaning processes are performed in order to remove the circle defect 145 prior to the cleaning and pad treatment processes, the circle defect 145 remains. Since the ashing step and the solvent cleaning step are performed during the cleaning process, the external appearance of the pad may be relatively rough and may be not clear.
FIG. 1D shows a state in which a pad protection layer 150 has been deposited. FIG. 1E shows a state in which a color filter array layer 160 has been deposited. FIG. 1F shows a color filter array 165 formed through a color photo process. FIG. 1G shows a planarization layer 170 formed through a photo process. FIG. 1H shows a convex micro-lens 180 which is formed through a thermal reflow process. FIG. 1I shows the pad 110 exposed by etching the pad protection layer 150 to enable a probing test. The final curing step is performed after the ashing step and the solvent cleaning step in the cleaning process. Since the curing step, which is a kind of heat treatment step, is performed when the pad is exposed through solvent cleaning, defects occur in the external appearance of the pad.